The primary goal of this study is to conduct a comprehensive investigation of priapism in boys and young men with sickle cell disease (SCD). As such, it represents the initial step toward defining an effective way to manage priapism, and to reduce the frequency of impotence that is its major complication in adult males with SCD. The aims of this proposal are: 1) to conduct a Iongitudinal cohort study in order to define the incidence of priapism in relationship to the physical and hormonal developmental stages of puberty and early maturity, to explore the relationship between priapism and psychological adjustment; and 2) to conduct a pilot, placebo-controlled intervention trial in which the ability of pseudoephedrine to prevent priapism will be evaluated. The first stage of this proposal involves an observational study that will be open to all boys and young men with SCD between the ages of 7 -29 years. They will keep daily records of the occurrence of priapism, and will be admitted every 6 months for an intensive evaluation of physical growth, genital pubertal stage, body composition, bone age, gonadotropins, testosterone, insulin-like growth factor and nocturnal penile tumescence. During these admissions, the participants will also complete several psychological assessments. Data from this phase will be used to identify the association (if any) between priapism and pubertal stage, gonadotropin levels, and testosterone concentration. The data will also determine if there is a relationship between priapism and psychological adjustment. The second stage of this proposal will seek to enroll those individuals who are found to have qualifying episodes of priapism on to a randomized, double-blinded, placebo-controlled clinical trial of pseudoephedrine. The purpose of this pilot study is to determine whether pseudoephedrine is able to prevent episodes of priapism. During this trial, each participant will continue to keep the same daily journal. In addition, each participant will be admitted at the beginning and end of the trial to complete the same physical, hormonal and psychological assessments as were performed in the observational phase. The outcome measures of the prevention trial will be the occurrence of priapism, duration of priapism and the interval between episodes of priapism. In addition, physical growth, secondary sexual development, body composition and psychological adjustment will be compared between the treatment arms. The data collected will establish the feasibility of certain key methods, and will provide estimates of rates, standard deviations, median time-to-event. These results, which are absolutely essential before a large scale treatment trial can be planned, will provide the biological and statistical background for future work in this field.